Field of the Invention
The present invention relates to an aqueous ink, an ink cartridge, and an ink jet recording method.
Description of the Related Art
In recent years, inks containing pigments as coloring materials (pigment inks) have been widely used as an ink used for an ink jet recording method. Such pigment inks are required to enable recording of high-quality images comparable to silver halide photographs. In addition, with improved image quality of recorded images, higher recording speeds are also demanded.
Pigments are, however, present in the form of particles in inks, and thus images recorded with the pigment inks unfortunately have lower glossiness than that of images recorded with dye inks in which dyes are dissolved in an aqueous medium. In order to meet the demand for higher image quality of images to be recorded, various functional materials such as a fluorinated surfactant are added to the pigment inks. When a pigment ink containing the functional material is applied to a recording medium, the pigment and the functional material are deposited on the surface of the recording medium. This reduces the permeability of an ink that is subsequently applied onto the pigment layer to cause such a beading phenomenon that dots of the ink spread to be locally connected to each other, resulting in generation of density unevenness in the resulting image. If the beading is caused, it will be visually observed that unevenness seems to be generated in the solid image.
To solve this problem, various techniques have been disclosed. For example, an ink containing a particular yellow pigment, a water-soluble acrylic resin, a water-soluble urethane resin, a polyoxyethylene alkyl ether having an HLB value of 13 or more, and a water-soluble organic solvent such as triethylene glycol has been disclosed (Japanese Patent Application Laid-Open No. 2012-072359). Moreover, an ink that contains a dipeptide and an anionic fluorinated surfactant containing a lower perfluorohydrocarbon group has been disclosed. This ink can improve image density, fixability, and ink drying properties (Japanese Patent Application Laid-Open No. 2011-190406).
An ink jet recording system using a fixer fluid containing a cationic polymer and an acidic precipitant and using an ink containing an anionic pigment, a nonionic surfactant, an anionic binder, and an organic solvent has also been disclosed (Japanese Patent Application Laid-Open No. 2006-159907). Furthermore, an ink for ink jet recording containing a pigment, a styrene copolymer having a hydrophilic group and functioning as a pigment dispersant, a binder, and water has been disclosed (Japanese Patent Application Laid-Open No. 2013-082885).